1. Field of the Invention
This invention relates to the field of oil field tools. More specifically, the invention relates to a flow activated valve that allows its closure without pressure surge.
2. Background of the Invention
Oil field wells are typically drilled using a conduit, such as drill pipe or coiled tubing, attached to a certain tool designed for a particular operation. During deployment of the tool in the well, drilling fluid flows through the conduit and the tool to wash debris through an annulus formed between the conduit and a wall of the wellbore to the surface. This operation typically involves high rates of fluid flow.
After the tool has been deployed to a desired location, the fluid passage of the tool is closed, and the drilling fluid pressure is raised to a sufficient level to operate the tool. Typically, a sealing member, such as a dart or a ball, is pumped through the conduit into the tool to provide a seal to close the fluid passage. However, the passage diameter of the conduit usually is significantly larger than the passage diameter of the tool, which makes use of a dart or a ball for tool fluid passage closure unreliable or impossible.
Another type of sealing member is a flow activated shut off valve. This type of valve allows a certain flow rate of drilling fluids to pass through the tool during tool deployment when the valve is open. To close the valve, the flow rate is increased to a higher level so that backpressure develops and urges the valve into a closed position. A problem with existing flow actuated shut off valves is that the valve closure is almost instantaneous, which may result in a high pressure surge, or, so called water hammer effect, that may damage tool components or cause the conduit, such as coiled tubing, to burst.
Thus, there is a need for a reliable sealing member that allows a high circulation flow rate through the tool during deployment and provides closure of the fluid passage of the tool without causing a pressure surge.